Art of spray drying soap



Patented Jan. 1, 193s lUNITED STATES PATENT OFFICE 7 Claims. (Cl. 87-16)My invention relates to the art of spray drying soap, and particularlyto the art of controlling the bulking weight of spray dried soapparticles while maintaining a substantially uniform moisture content inthe finished particles, and while maintaining a uniform temperature ofthe gaseous medium introduced into the apparatus for drying and puffingthesoap particles.-

. In the spray drying of soap, particularly as taught by Holliday andLamont, the soap particles are preferably dried in a concurrent heatedgas supply which passes through the apparatus in the general directionof the spray of soap being dried.

Where there is any suggestion as to control of .the density vof thedried products, as far as I am y aware such controls have been byvaryingthe temperature of the drying gas. Lamont, for example, in his Patent#1,734,260 especially provides for the control of the density of thefinished product by varying the temperature of the hot gas introducedinto the drying chamber at the top ofthe tower. Thediiliculty withcontrolling the density of the finishedxproduct by varying thetemperature of the drying gas is that while a desired density may beobtained by such variation in the temperature ofthe drying gas, it doesnot necessarily `iollow that a desired moisture content will result. Forexample, when a more dense product is desired and the temperature of thedrying gas is lowered, the soap particle will not be pued out so much,and will consequently occupy a lesser volume for a given amount of soap.Due, however, to the fact that the amount of soap is compressed into asmaller particle, that is a thicker shell particle, it is more dicult todry it -toa moisture content suiliciently low as to prevent sticking andpacking of the powder as it is taken from the bottom of the. dryingtower. This objection may be overcome in a concurrent drying tower byatomizing the iiuid much liner so that the individual particles will besmaller and have a greater amount of surface from which moisture mayescape for a given weight of soap. Under such conditions,'a loweredtemperature will result in a proper con- 45 trol of the moisturecontent, but it will be noted that such a method of control requires twovariables to be accurately governed-first, the temperature of theincoming gas, and second, the degree of neness at .which the soap issprayed. 5 Further when the spray becomes too minute, the resultingpowder may be too dusty for practicable commercial purposes. Thepracticable density range on a strictly concurrent tower is between' .1and .3 specic gravity as compared with water, with the moisture contentbetween 5 and 15%,

and with the particle size such that at least of the product will remainon a s ixty mesh screen.

It is the object of my linvention to provide a method of spray drying inwhich a xed quantity of drying gas heated to a substantially uniformtemperature is employed, and in which the particlessprayed are of a sizesubstantially .35 mm. in diameter, with a weight of substantially ,.03mg.

It is my object in a spray drying tower to control variations in bulkingweight while maintaining a normal satisfactory'moisture content bycontrolling the elevation in the tower at which the drying gases are`introduced. l

` I propose, by means of controlling the level at which the drying gasesare introduced into the drying tower, to vary the density range of the.dried soap product between speciiic gravity las compared with water of.10 to .50, and at the same time to control the moisture content of thefinished product between 5 and 12%. It is a further characteristic of myproposed process that both the density and moisture can be varied overquite a wide range without varying the weight of the particles greatly.

Another object of my invention is to economize in thev heat unitsrequired to dry the product by returning some of the gas as it is drawnfrom the tower back again into the tower so.that the heat units thereinmay be utilized for their drying effect on the sprayed soap after thesoap particles have passed through the zone of exposure to the regularincoming supply of heated drying gas.

The above objects and other objects to which reference will be made inthe ensuring description, I accomplish by that certain combination andarrangement of parts' and by the various controls of the elevation ofthe incoming drying gas as hereinafter specified.

Referring to the drawing:-

Figure l is a diagrammatic plan view of a proposed dryingv tower.

Fig. 2 is a diagrammatic sectional view showing the drying apparatusindicated in Fig. 1.

I have shown a spray drying tower 1 of dimensions of approximatelytwenty feet in diameter, with a height of about sixty feet. The towerhas a conical'bottom 2 provided with a gas-sealed discharge valve 3, bywhich'the product-is discharged from the drying tower into conduit 4,where, by means of a suction fan 5, it is drawn into a separatingchamber 6, having a gas-sealed feed valve v7, which. feeds the powderinto a hopper 8, -from which it is dispensed in desired quantities toconveyors or to filling machines.

A gas heater 9 isshown, which may be a furnace, fired-preferably byeither oil or gas, from which the combustion gases pass directly to thetower. It may further be a heat exchanger supplied with steam or'othermeans for heating the incoming air or gas. A blower fan 10 blows gasthrough a conduit 11. At different elevations in the tower there areplenum chambers. The plenum chambers are annular conduits extendingaround the tower with openings through which the gas is blown into thetower.

In the diagrammatic illustration I have shown the top chamber 12 havingdischarge openings 13, through which gas is discharged into. the tower,and with a gate valve 14 between the conduit 11 and the plenum chamberso that the supply of gas may'be cut ofi if desired.

I have further shown the plenum chamber 15 having inlet openings 16, andwith a valve 17 for cutting off the gas supply to the middle plenumchamber.

The bottom plenum chamber 18 has gas admission ports 19, and a valve 20controlling the entrance of gas from the conduit 11. The bottomplenumchamber further has a valve 21, which controls the re-introduction of aportion of the heated waste gases drawn from conduit 24, through conduit23, by means of fan 22. The remaindenof the heated waste gases are drawnfrom conduit 24 through conduit 35 to separator 26 by means of fan 25.

A valve 27 controls the flow of separated powder from a separator 26 tothe conduit 4, from which any separated powder is discharged into thechamber 6, where it is mixed with the product being drawn up through theconduit 4. The

other ingredients, such as silicate of soda, salsoda, or other`builders, and the soap from the crutcher is pumped with a pump 30through the pipe 31 to the spray nozzles 32. The pump 30 is preferablyof a type in which the speed may be controlled either by a variablespeed motor, or by other suitable mechanical means. A steam jacket 33 isalso indicated for controlling' the temperature at which the soap ispumped to the spray nozzles.

In order to explain how I propose to control the bulking weight whilemaintaining a desired moisture content, and while pumping a fixed supplyof gas at a temperature of substantially from 400 to 500 degrees F., Ihave indicated zones A, B and C, in the drying tower, zone A being theportion between the plenum chamber 12 and the top of the tower; zone Bthe portion between the plenum chambers 15 and 12, and zone C theportion between the plenum chambers 18 and 15.

Any desired type of atomizer that will give the desired size of particlemay be used. The conventional type of pressure nozzle has been foundsatisfactory. 'Y i The control of the Aspray drying of soap is proceededwith as follows: Hot gas from the heater .the heated gas is introducedinto the plenum chamber 12 and passes into zone A, in which it meets thesprayed soap sprayed into zone A from the nozzles `32. The temperatureof the soap spray may vary between and 220 F., depending on theyviscosity of the soap and the ease with which it zsprays. A desirabletemperature for spraying the soap has been found to be about 200 F. Asthe sprayed soap falls through zone A, which is maintained at high'temperature, it is puffed out due to the rapid heat transfer caused bythe high gas temperature and the high moisture content of the soap, andthe individual particles rapidly assume the size vand shape which theyretain until they are discharged out of the bottom of the tower. Theparticles, however, will not be completely dried in zone-A, and willcontain variable quantities of moisture considerably above thatcontained in the final product.

As has been stated, some of the exhaust gas from the conduit 24 is blownback into the tower,

. The sprayed, partially dried particles of soap falling from zone Athrough the rising counter- -current gases moving up through zones C andB,

will be further dried to a moisture content of substantially 8%, and thefinished product, as it is fed out through the gas locked valve 3 `willhave a temperature of about 180 F. During the passage of the productthrough the gas conveyor the temperature is further substantiallyreduced.

After establishing the proper operating conditions for each tower, thesize and number of nozzles, etc., that will give a bulk density of about.10 to .20 when the heated gas is introduced into zone A with thedesired weight ofparticle, then without changing operating conditionsexcept to introduce the hot gas into zone B instead of into zone A, aproduct with bulk density of about .20 to .30 will be obtained. Likewisewithout changing operating conditions except to introduce the heated gasinto zone C a product with bulk density of about .30 to .50 will beobtained.

To control the bulk density closely to a desired figure within the rangementioned for each zone, the quantity of. s'oap atomized and thetemperature of the heated gas may be varied slightly, but the maincontrol to obtain products having bulk density within the three rangesmentioned is by introducing the heated gas at three differentelevations, as stated, and as shown the recirculated drying' gas istaken from above the middle of the tower and reintroduced below themiddle of the tower.

It appears from the above description that when the hot gas enters atzone A the sprayedpar- -ticles immediately come in contact with thehottest gas and are thereby heated and dried quickly with consequentpuffing and therefore a product of low bulk density is obtained. Whenthe hot gas enters at zone B, the sprayed particles do not come incontact with the hottestgas until,

they have' previously passed through zone A where the gas has lost someof its original heat, and

therefore the particles are heated and dried more gradually and they donot puit so much. thus giv- ,y ing a product of higher lulkdensitythanwhen the hot gas is introduced at zone A. In both these cases theparticles are further dried, but without further puiling, by fallingthrough the recirculated exhaust gas which is introduced at zone C. Whenthe hot gas and a portion of the exhaust gas are both introduced at zoneC the two gases are preferably mixed before entering the tower, and thenthe sprayed particles are heated and dried still more gradually thanwhen the hot gas is introduced at higher elevations, and

less pufng occurs, thus giving a product of still,

higher bulk density. In these cases thus de-fy scribed, except when thehot gas is introduced directly into zone A, thetemperature of the gaswhen it comes in contact with the freshly sprayed soap in zone A hasbeen so reduced that it is not high enough to cause the rapidvaporization necessary to 'pulling particles so as to produce a productof lowest bulk density.

It should be particularly noted that the func tion of the recirculatedgas is really twofold-mst the heat economy due to using exhaust or wastegas, and secondly, the effect of lowering the temperature of the gas asit passes through thetower without reducing the total quantity of heatintroduced into the tower.

By the use of my novel method of spray drying in a counter current ofheated drying gas I have produced soap powders with densities varyingbetween .10 and .50 without varying either the weight of the particlesof soap as sprayed, without appreciable variation in the temperature orrate of introduction of the incoming heated gas, arid withoutessentially varying the moisture content in the finished product.

Having thus described my invention, what I g claim as new and desire tosecure by Letters Patent, is:

1. In -the spray drying drying tower, the method of controlling the bulkdensity -of the dried product which consists in spraying the soapdownwardly in the tower, in substantially uniformly sized particles inintroducing a counter current of heated drying gas into the tower andcontrolling the elevation within the tower at which ythe drying gas isintroduced, and returning a portion of the e'xhaust gas into the bottomof the tower.

2. A soap spray drying process which consists in forcing soap through aspray ynozzle at a pressure of from 250 to 750 pounds per square inch,causing the sprayed soap to bedischarged into a definite volume ofacounter currentof heated drying. gas and controlling. the bulkingdensity of the spray dried product by controlling the elevation at whichthe heated drying gas is introduced. v Y

3. In the art of spray drying soap, a method of controlling the bulkingdensity of the spray dried product while'maintaining the sprayedparticles at a substantially uniform weight and moisture of soap in aspray tower so that the exposure of the particles to the drying gas atthe level at which said drying gas is introduced will be such -that adesired bulk density will be obtained. Y

4. In the spray drying of soap in a spray drying tower, themethod ofcontrolling the bulk density of the dried product to any desired pointbetween 0.10 and 0.50, which consists in spraying the soap from above sothat it falls downwardly in the tower througha rising counter-current ofVfresh heated drying lgas of substantially uniform volume andtemperature so controlled and intro-i duced into the tower at variouspredetermined distances below the spraying nozzles, so as to puff theparticles to the desired bulk density.

5. In the spray drying of soap in a spray drying tower, the method ofcontrolling thebulk density of dried product without changing themoisture content o'f the product, which consists in spraying the soapfrom above so that it yfalls downwardly in the tower through arisingcounter-current of fresh heated drying gas of substantiallyuniform volume and temperature so controlled and introduced into thetower at various predetermined distances below the spraying nozzles, soas to puif the particles to the desired the required w fresh heateddrying gas of substantially uniform .volume and temperature at variouspredetermined distances below the spraying nozzles, and recirculating aportion of the exhaust gas .from

to various predetermined levels, while controlling the level ofintroducing the fresh drying gas so as to puff the particles to thedesired bulk density.

'1. In the spray drying of soap in a spray drying tower, the method ofcontrolling the bulk density of the dried product to any desired pointbetween, 0.10 and 0.50, which consists in spraying the soap from aboveso that it falls downwardly in the tower, introducing a ,rising lcounter-current of fresh heated drying gas of substantially uniformvolume and temperature at various predetermined distances below therspraying nomles, and recirculating a portion of the exhaust gas fromthe tower and re-introducing it into the tower at a level below that ofthe fresh heating gas, while controlling the level of introducing thefresh drying gas to various. predetermined levels so that the sprayedsoap particles are first puffed to the desiredl size and partially driedbyv contact with the mixture of fresh heated drying gas and recirculatedgas, and theny further dried by contact with the recirculated gas aloneto obtain the desired final moisture content and the desired bulkdensity.

' THOMAS EDWARD

